Sydney will host a major international summit to counter violent extremism this week, but some key countries including Indonesia will be represented at the relatively junior level of officials rather than ministers.

Prime Minister Tony Abbott will on Thursday morning open the gathering, which will focus on combating extremist propaganda and involve participants from about 25 countries.

Prime Minister Tony Abbott will open a major international summit to counter violent extremism this week. Photo: Alex Ellinghausen

However, Jakarta, despite being Australia's most important regional partner on counter-terrorism, would not be represented by a minister, nor by the head of the National Counter-Terrorism Agency, a spokesman for the Indonesian embassy said.

Instead, it is sending a director, Herry Sudrajat, who is not the most senior person at the agency.

The Indonesian Embassy spokesman said Ambassador Nadjib Riphat Kesoema would also attend the summit. He denied there was any "snub" intended, insisting "we are not sending any message like that".

The nation's most senior counter-terrorism official had planned to attend but instead had been asked specifically by President Joko Widodo to go to another "special event", the spokesman said.

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"We think that this counter-terrorism event is very important," he said.

Relations between Canberra and Jakarta have been strained since the executions of Bali nine drug smugglers Andrew Chan and Myuran Sukumaran.

Countries that will be represented by ministers include Malaysia, Cambodia, Japan, Laos, Singapore, South Korea, Vietnam and New Zealand.

Most countries will send ambassadors or officials, including the United States, China, Britain, Russia, India, the Philippines, Sri Lanka, Egypt and Thailand. The United Nations and the European Union will also have delegates.

Attorney-General George Brandis will host the summit and Foreign Minister Julie Bishop will deliver a speech on the role of women and families in countering extremist narratives.

When he announced the summit last month, Senator Brandis said the focus would be to "identify and develop practical resources and strategies to address the shared threat posed by terrorist propaganda and exploitation of the internet".

He said the Islamic State terror group alone was responsible for spreading at least 100,000 pieces of online propaganda each day.

The summit would build on previous work at a similar event hosted by the White House in February, which Senator Brandis attended along with about 60 ministers from around the world.

It will report on its work to the United Nations General Assembly leaders meeting in September, where counter-terrorism will be a focus.

The Australian Federal Police has counter-terrorism co-operation teams in Indonesia and the Philippines and a training and development centre in Thailand, which support those countries in counter-terrorism investigations.